Variable rate shading

ABSTRACT

Methods and devices for rendering graphics in a computer system include a graphical processing unit (GPU) with a flexible, dynamic, application-directed mechanism for varying the rate at which fragment shading is performed for rendering an image to a display. In particular, the described aspects include determining, at a rasterization stage, map coordinates based on coarse scan converting a primitive of an object, the map coordinates indicating a location on a sampling rate parameter (SRP) map of a fragment within the primitive of the object, and identifying a lookup value for the fragment within the primitive of the object based at least on map coordinates, and calculating a respective fragment variable SRP value for the fragment within the primitive of the object based at least on the lookup value.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application for patent is a related to U.S. application Ser.No. 15/237,334 entitled “VARIABLE RATE SHADING” filed Aug. 15, 2016, andclaims priority to U.S. Application No. 62/460,496 entitled “VARIABLERATE SHADING” filed Feb. 17, 2017, both of which are assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

The present aspects relate to a computer device, and more particularly,to performing variable sample rate shading in rendering graphics on acomputer device.

Computer graphics systems, which can render 2D objects or objects from a3D world (real or imaginary) onto a two-dimensional (2D) display screen,are currently used in a wide variety of applications. For example, 3Dcomputer graphics can be used for real-time interactive applications,such as video games, virtual reality, scientific research, etc., as wellas off-line applications, such as the creation of high resolutionmovies, graphic art, etc. Typically, the graphics system includes agraphics processing unit (GPU). A GPU may be implemented as aco-processor component to a central processing unit (CPU) of thecomputer, and may be provided in the form of an add-in card (e.g., videocard), co-processor, or as functionality that is integrated directlyinto the motherboard of the computer or into other devices, such as agaming device.

Typically, the GPU has a “logical graphics pipeline,” which may acceptas input some representation of a 2D or 3D scene and output a bitmapthat defines a 2D image for display. For example, the DIRECTX collectionof application programming interfaces by MICROSOFT CORPORATION,including the DIRECT3D API, is an example of APIs that have graphicpipeline models. Another example includes the Open Graphics Library(OPENGL) API. The graphics pipeline typically includes a number ofstages to convert a group of vertices, textures, buffers, and stateinformation into an image frame on the screen. For instance, one of thestages of the graphics pipeline is a shader. A shader is a piece of coderunning on a specialized processing unit, also referred to as a shaderunit or shader processor, usually executing multiple data threads atonce, programmed to generate appropriate levels of color and/or specialeffects to fragments being rendered. In particular, for example, avertex shader processes traits (position, texture coordinates, color,etc.) of a vertex, and a pixel shader processes traits (texture values,color, z-depth and alpha value) of a pixel. The prior art typically usesa constant sampling rate within the graphics pipeline for rendering anentire frame. Because of the desire for high-fidelity images, pixelshading is typically performed at a per-pixel rate, or at the rate of Nsamples per pixel if N-multisample anti-aliasing is required. Thus, thecomputer device operates the graphics pipeline to convert informationabout 3D objects into a bit map that can be displayed, and this processrequires considerable memory and processing power.

There are continuing increases in pixel density and display resolution,and a continuing desire for power reduction in mobile display devices,like the HOLOLENS holographic headset device by MICROSOFT CORPORATION.Therefore, there is a need in the art for more efficient graphicsprocessing in a computer device.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

One aspect relates to a method of rendering graphics in a computersystem, including determining, by a GPU at a rasterization stage, mapcoordinates based on coarse scan converting a primitive of an object,the map coordinates indicating a location on a sampling rate parameter(SRP) map of a fragment within the primitive of the object. Further, themethod includes identifying, by the GPU at the rasterization stage, alookup value for the fragment within the primitive of the object basedat least on the map coordinates. Further, the method includescalculating, by the GPU at the rasterization stage, a respectivefragment variable SRP value for the fragment within the primitive of theobject based at least on the lookup value. Additionally, the methodincludes shading, by the GPU at a pixel shader stage, the fragmentwithin the primitive of the object based on the respective fragmentvariable SRP value.

In another aspect, a computer device includes a memory and a graphicsprocessing unit (GPU) in communication with the memory. The GPU isconfigured to determine, at a rasterization stage, map coordinates basedon coarse scan converting a primitive of an object, the map coordinatesindicating a location on a SRP map of a fragment within the primitive ofthe object. Further, the GPU is configured to identify, at therasterization stage, the lookup value for the fragment within theprimitive of the object based at least on the map coordinates. Further,the GPU is configured to calculate, at the rasterization stage, arespective fragment variable SRP value for the fragment within theprimitive of the object based at least on the lookup value.Additionally, the GPU is configured to shade, at a pixel shader stage,the fragment within the primitive of the object based on the respectivefragment variable SRP value.

In a further aspect, a computer-readable medium storingcomputer-executable instructions executable by a processor for renderinggraphics in a computer device includes various instructions. Thecomputer-readable medium includes instructions for determining, by a GPUat a rasterization stage, map coordinates based on coarse scanconverting a primitive of an object, the map coordinates indicating alocation on a SRP map of a fragment within the primitive of the object.Further, computer-readable medium includes instructions for identifying,by the GPU at the rasterization stage, a lookup value for the fragmenswithin the primitive of the object based at least on the mapcoordinates. Also, the computer-readable medium includes instructionsfor calculating, by the GPU at the rasterization stage, a respectivefragment variable SRP value for the fragment within the primitive of theobject based at least on the lookup value. Additionally, thecomputer-readable medium includes instructions for shading, by the GPUat a pixel shader stage, the fragment within the primitive of the objectbased on the respective fragment variable SRP value.

Additional advantages and novel features relating to aspects of thepresent invention will be set forth in part in the description thatfollows, and in part will become more apparent to those skilled in theart upon examination of the following or upon learning by practicethereof.

DESCRIPTION OF THE FIGURES

In the drawings:

FIG. 1 is a schematic block diagram of an example architecture of acomputer device including a graphics processing unit and a graphicspipeline configured according to the described aspects;

FIG. 2 is a schematic diagram of an example of the graphics pipeline andgraphics memory of the computer device of FIG. 1;

FIG. 3-1 is a flowchart of an example of a method of rendering an imagebased on operation of the graphics pipeline according to the describedaspects;

FIG. 3-2 is a flowchart of another example of a method of rendering animage based on operation of the graphics pipeline according to thedescribed aspects;

FIG. 4 is a schematic diagram of an example of a primitive of an image,and tiles and sub-tiles covered by the primitive, and an example of arasterizer stage component and subcomponents associated with theoperation of the rasterization stage in the method of FIGS. 3-1 and 3-2;

FIG. 5 is a graph of an example primitive having respective verticeseach having a respective sample rate parameter (SRP) value, andidentifying additional points per tile (e.g., at an intersection withthe primitive and/or at corners of the respective tile) from which SRPvalues may be determined based on interpolation from the correspondingvertex-specific SRP values;

FIG. 6 is a table listing tiles and a formula for choosing acorresponding maximum sample rate parameter (SRP) value for therespective tile from among SRP value corresponding to particular pointscorresponding to the respective tile, according to the describedaspects;

FIG. 7 is a close-up view of the graph of FIG. 6, and additionallyincluding sub-tile grids for one of the tiles of FIG. 6 and samplepositions per pixel in each box of the sub-tile grid, and furtheridentifying different shading rates for different sets of pixels in thesub-tile grid, according to the described aspects;

FIG. 8 is a graph of an example of calculating texture gradients foreach pixel of a sub-tile grid, according to the described aspects;

FIG. 9 is a graph of an example of modifying the calculated texturegradients of the graph of FIG. 8 by the tile-specific orfragment-specific SRP value determined according to the describedaspects;

FIG. 10 is an example of calculating fragment variable SRP values forfragments of a coarse SRP map during a rasterization stage in the methodof FIGS. 3-1 and 3-2, according to the described aspects;

FIG. 11 is a flowchart of a method of rendering an image on a computerdevice, which encompasses the method in the flowchart of FIG. 2; and

FIG. 12 is an example of an image generated by the computer device ofFIGS. 1 and 2, and overlaying the image a representation of a grid oftiles, wherein different ones of the tiles have different shading ratesas determined according to the described aspects.

DETAILED DESCRIPTION

The described aspects provide a graphical processing unit (GPU) with aflexible, dynamic, application-directed mechanism for varying the rateat which fragment shading is performed for rendering an image to adisplay. In particular, the described aspects allow different shadingrates to be used for different fragments (e.g., tile, sub-tile, quad,pixel, or sub-pixel region) of a rasterized (scan converted) primitiveused to render the image. For instance, the described aspects may allowthe shading rate to vary from very coarse (i.e., one shaded sample per8×8 pixel screen tile) to quad based (i.e., one shaded sample per 2×2pixel area), or finer (i.e., one shaded sample per pixel), to fullsubpixel resolution.

In determining the shading rate for different regions of each primitive(and/or different regions of the 2D image), the described aspects takeinto account variability with respect to desired level of detail (LOD)across regions of the image. For instance, but not limited hereto,different shading rates for different fragments of each primitive may beassociated with one or more of foveated rendering (fixed or eyetracked), foveated display optics, objects of interest (e.g., an enemyin a game), and content characteristics (e.g., sharpness of edges,degree of detail, smoothness of lighting, etc.). In other words, thedescribed aspects, define a mechanism to control, on-the-fly (e.g.,during the processing of any portion of any primitive used in the entireimage in the graphic pipeline), whether work performed by the pixelshader stage of the graphics pipeline of the GPU is performed at aparticular spatial rate, based on a number of possible factors,including screen-space position of the primitive, local scenecomplexity, and/or object identifier (ID), to name a few.

More specifically, the described aspects control respective shadingrates for different regions of each primitive (and/or of each 2D image)based on a new, interpolated shading rate parameter for use by arasterization stage of the graphics pipeline. For instance, therasterization stage utilizes one or more shading rate parameter valuesto determine how many samples to shade for each corresponding region ofa given primitive. In other words, the described aspects enable therasterizer to change shading rates on-the-fly (e.g., processing anentire image at one time, for instance, without having to performdifferent rendering passes or without having to render the sameprimitive into multiple viewports) as it scan-converts each primitive.Additionally, in combination with determining how many samples to shade,or independently, the rasterization stage utilizes each respectiveshading rate parameter to determine how many sample positions toconsider to be covered by the computed shaded output, e.g., the fragmentcolor. In other words, the described aspects enable the rasterizer to“boost” the coverage of the computed shaded output by allowing the colorsample to be shared across two or more pixels. The specific actionsrelated to determination and utilization within the graphics pipeline ofthis new shading rate parameter are described below in detail.

In some cases, implementation of the described aspects may allow theamount of shading and texturing work within the graphics pipeline to bereduced by as much as a factor of 1024 (e.g., for an 8×8 tile, 64pixels*16 samples=1024) on a typical GPU.

Optionally, the described aspects may additionally provide an ability toadjust the texture LOD gradient for mipmap LOD determination in a way tocorrespond to the number of samples shaded in a particular region.Typically texture coordinates are calculated for each pixel in a 2×2region of pixels in order to derive a gradient, but if only one sampleis needed in that 2×2 region, this is wasteful. As such, in one option,the described aspects may run a new shader prologue stage, which mayalso be referred to as a gradient shader, before performing the rest offragment shading. In this case, the gradient shader does limited work atpixel granularity just to compute texture gradients.

In some further optional cases, the described aspects may includefurther optimizations to allow a variety of ways to specify the set offrame buffer pixels and multi-samples that are to be covered by thecolor value produced.

Additionally, in some examples, it may desirable to perform increased orreduced rate shading over a larger area of an image, such as a screenspace (e.g., a statically or dynamically defined region of the image),the entire image, etc. For example, screen space variable rate shading(SSVRS) may be performed in instances such as variable rate shading,motion blurred screens, cut scenes, etc. Accordingly, for example inorder to perform SSVRS, a GPU may bind a bitmap (e.g., screen spacetexture) to a scan converter (i.e., rasterizer stage). The bitmap may belooked up based on one or more bits of screen or viewport x,ycoordinates.

Referring to FIG. 1, in one example, a computer device 10 includes agraphics processing unit (GPU) 12 configured to implement the describedaspects of variable rate shading. For example, GPU 12 is configured todetermine and use different fragment shading rates for shading (i.e.calculating a color for) different fragments covered by a primitive ofan image based on respective shading rate parameters for respectiveregions of the image. In other words, GPU 12 can dynamically vary therate at which fragment shading is performed on-the-fly during renderingof an image, for example, based on a variability in level of detail(LOD) within the image. Alternatively, or in addition, GPU 12 can beconfigured to vary a number of samples (e.g., nSamples, such as colorsamples) for each pixel of the image based on the respective shadingrate parameters for respective regions of the image. In other words, GPU12 can use a coverage mask for each shaded color fragment that enablessharing the shaded color fragment across the samples of two or morepixels.

For example, in one implementation, computer device 10 includes a CPU34, which may be one or more processors that are specially-configured orprogrammed to control operation of computer device 10 according to thedescribed aspects. For instance, a user may provide an input to computerdevice 10 to cause CPU 34 to execute one or more software applications46. Software applications 46 that execute on CPU 34 may include, forexample, but are not limited to one or more of an operating system, aword processor application, an email application, a spread sheetapplication, a media player application, a video game application, agraphical user interface application or another program. Additionally,CPU 34 may include a GPU driver 48 that can be executed for controllingthe operation of GPU 12. The user may provide input to computer device10 via one or more input devices 51 such as a keyboard, a mouse, amicrophone, a touch pad or another input device that is coupled tocomputer device 10 via an input/output bridge 49, such as but notlimited to a southbridge chipset or integrated circuit.

The software applications 46 that execute on CPU 34 may include one ormore instructions that executable to cause CPU 34 to issue one or moregraphics commands 36 to cause the rendering of graphics data associatedwith an image 24 on display device 40. The image 24 may comprise, forexample, one or more objects, and each object may comprise one or moreprimitives, as explained in more detail below. For instance, in someimplementations, the software application 46 places graphics commands 36in a buffer in the system memory 56 and the command processor 64 of theGPU 12 fetches them. In some examples, the software instructions mayconform to a graphics application programming interface (API) 52, suchas, but not limited to, a DirectX and/or Direct3D API, an Open GraphicsLibrary (OpenGL®) API, an Open Graphics Library Embedded Systems (OpenGLES) API, an X3D API, a RenderMan API, a WebGL API, or any other publicor proprietary standard graphics API. In order to process the graphicsrendering instructions, CPU 34 may issue one or more graphics commands36 to GPU 12 (e.g., through GPU driver 48) to cause GPU 12 to performsome or all of the rendering of the graphics data. In some examples, thegraphics data to be rendered may include a list of graphics primitives,e.g., points, lines, triangles, quadrilaterals, triangle strips, etc.

Computer device 10 may also include a memory bridge 54 in communicationwith CPU 34 that facilitates the transfer of data going into and out ofsystem memory 56 and/or graphics memory 58. For example, memory bridge54 may receive memory read and write commands, and service such commandswith respect to system memory 56 and/or graphics memory 58 in order toprovide memory services for the components in computer device 10. Memorybridge 54 is communicatively coupled to GPU 12, CPU 34, system memory56, graphics memory 58, and input/output bridge 49 via one or more buses60. In an aspect, for example, memory bridge 54 may be a northbridgeintegrated circuit or chipset.

System memory 56 may store program modules and/or instructions that areaccessible for execution by CPU 34 and/or data for use by the programsexecuting on CPU 34. For example, system memory 56 may store theoperating system application for booting computer device 10. Further,for example, system memory 56 may store a window manager applicationthat is used by CPU 34 to present a graphical user interface (GUI) ondisplay device 40. In addition, system memory 56 may store userapplications 46 and other information for use by and/or generated byother components of computer device 10. For example, system memory 56may act as a device memory for GPU 12 (although, as illustrated, GPU 12may generally have a direct connection to its own graphics memory 58)and may store data to be operated on by GPU 12 as well as data resultingfrom operations performed by GPU 12. For example, system memory 56 maystore any combination of texture buffers, depth buffers, stencilbuffers, vertex buffers, frame buffers, or the like. System memory 56may include one or more volatile or non-volatile memories or storagedevices, such as, for example, random access memory (RAM), static RAM(SRAM), dynamic RAM (DRAM), read-only memory (ROM), erasableprogrammable ROM (EPROM), electrically erasable programmable ROM(EEPROM), Flash memory, a magnetic data media or an optical storagemedia.

Additionally, in an aspect, computer device 10 may include or may becommunicatively connected with a system disk 62, such as a CD-ROM orother removable memory device. System disk 62 may include programsand/or instructions that computer device 10 can use, for example, toboot operating system in the event that booting operating system fromsystem memory 56 fails. System disk 62 may be communicatively coupled tothe other components of computer device 10 via input/output bridge 49.

As discussed above, GPU 12 may be configured to perform graphicsoperations to render one or more render targets 44 (e.g., based ongraphics primitives) to display device 40 to form image 24. Forinstance, when one of the software applications 46 executing on CPU 34requires graphics processing, CPU 34 may provide graphics commands andgraphics data associated with image 24, along with graphics command 36,to GPU 12 for rendering to display device 40. The graphics data mayinclude, e.g., drawing commands, state information, primitiveinformation, texture information, etc. GPU 12 may include one or moreprocessors, including a command processor 64 for receiving graphicscommand 36 and initiating or controlling the subsequent graphicsprocessing by at least one primitive processor 66 for assemblingprimitives, a plurality of graphics shader processors 68 for processingvertex, surface, pixel, and other data for GPU 12, one or more textureprocessors 67 for generating texture data for fragments or pixels, andone or more color and depth processors 69 for generating color data anddepth data and merging the shading output. For example, in an aspect,primitive processor 66 may implement input assembler and rasterizerstages of a logical graphics pipeline, as is discussed below. GPU 12may, in some instances, be built with a highly parallel structure thatprovide more efficient processing of complex graphic-related operationsthan CPU 34. For example, GPU 12 may include a plurality of processingelements that are configured to operate on multiple vertices or pixelsin a parallel manner. The highly parallel nature of GPU 12 may, in someinstances, allow GPU 12 to draw graphics image 24, e.g., GUIs andtwo-dimensional (2D) and/or three-dimensional (3D) graphics scenes, ontodisplay device 40 more quickly than drawing the image 24 directly todisplay device 40 using CPU 34.

GPU 12 may, in some instances, be integrated into a motherboard ofcomputer device 10. In other instances, GPU 12 may be present on agraphics card that is installed in a port in the motherboard of computerdevice 10 or may be otherwise incorporated within a peripheral deviceconfigured to interoperate with computer device 10. GPU 12 may includeone or more processors, such as one or more microprocessors, applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), digital signal processors (DSPs), or other equivalentintegrated or discrete logic circuitry.

In an aspect, GPU 12 may be directly coupled to graphics memory 58. Forexample, graphics memory 58 may store any combination of index buffers,vertex buffers, texture buffers, depth buffers, stencil buffers, rendertarget buffers, frame buffers, state information, shader resources,constants buffers, coarse SRP maps (e.g., a 2D map of a viewable area atcoarse resolution that can be used to look-up an SRP value based on aclosest point in the map to the transformed vertex), unordered accessview resources, graphics pipeline stream outputs, or the like. As such,GPU 12 may read data from and write data to graphics memory 58 withoutusing bus 60. In other words, GPU 12 may process data locally usingstorage local to the graphics card, instead of system memory 56. Thisallows GPU 12 to operate in a more efficient manner by eliminating theneed of GPU 12 to read and write data via bus 60, which may experienceheavy bus traffic. In some instances, however, GPU 12 may not include aseparate memory, but instead may utilize system memory 56 via bus 60.Graphics memory 58 may include one or more volatile or non-volatilememories or storage devices, such as, e.g., random access memory (RAM),static RAM (SRAM), dynamic RAM (DRAM), erasable programmable ROM(EPROM), electrically erasable programmable ROM (EEPROM), Flash memory,a magnetic data media or an optical storage media.

CPU 34 and/or GPU 12 may store rendered image data, e.g., render targets44, in a render target buffer of graphic memory 58. It should be notedthat the render target buffer also may be an independent memory or maybe allocated within system memory 56. GPU 12 may further include aresolver component 70 configured to retrieve the data from a rendertarget buffer of graphic memory 58 and convert multisample data intoper-pixel color values to be sent to display device 40 to display image24 represented by the rendered image data. In some examples, GPU 12 mayinclude a digital-to-analog converter (DAC) that is configured toconvert the digital values retrieved from the resolved render targetbuffer into an analog signal consumable by display device 40. In otherexamples, GPU 12 may pass the digital values to display device 40 over adigital interface, such as a High-Definition Multi-media Interface (HDMIinterface) or a DISPLAYPORT interface, for additional processing andconversion to analog. As such, in some aspects, the combination of GPU12, graphics memory 58, and resolver component 70 may be referred to asa graphics processing system 72.

Display device 40 may include a monitor, a television, a projectiondevice, a liquid crystal display (LCD), a plasma display panel, a lightemitting diode (LED) array, such as an organic LED (OLED) display, acathode ray tube (CRT) display, electronic paper, a surface-conductionelectron-emitted display (SED), a laser television display, ananocrystal display or another type of display unit. Display device 40may be integrated within computer device 10. For instance, displaydevice 40 may be a screen of a mobile telephone. Alternatively, displaydevice 40 may be a stand-alone device coupled to computer device 10 viaa wired or wireless communications link. For instance, display device 40may be a computer monitor or flat panel display connected to a personalcomputer via a cable or wireless link.

According to one example of the described aspects, graphic API 52 andGPU driver 48 may configure GPU 12 to execute logical graphics pipeline14 to perform variable rate shading as described herein.

Referring to FIG. 2, for instance, in one example, GPU 12 can beconfigured to implement the stages of an example logical graphicspipeline 14 that may to perform variable rate shading as describedherein. In an aspect, one or more of the various stages may beprogrammable, for instance, to utilize the new, interpolated SRP valuesdescribed above. Moreover, in an aspect, common shader cores may berepresented by the rounded rectangular blocks. This programmabilitymakes graphics pipeline 14 extremely flexible and adaptable. The purposeof each of the stages is now described in brief below, and additionalfunctionality will be further described with respect to subsequentfigures.

The input assembler stage 80 supplies data (triangles, lines, points,and indexes) to the pipeline. It also optionally processes shading rateparameters per object (SRPo), per primitive (SRPp), or per vertex(SRPv), generally referenced at 112, as determined by the application 46(FIG. 1). As generally indicated at 114, input assembler stage 80 mayoutput the SRPp, or an SRPv if the SRPv is not generated by a vertexshader stage 82.

The vertex shader stage 82 processes vertices, typically performingoperations such as transformations, skinning, and lighting. Vertexshader stage 82 takes a single input vertex and produces a single outputvertex. Also, as indicated at 110, vertex shader stage 82 optionallyinputs the per-vertex shading rate parameter (SRPv) or the per-primitiveshading rate parameter (SRPp) and typically outputs an SRPv, that iseither input or calculated or looked up. It should be noted that, insome implementations, such as when using higher-order surfaces, the SRPvcomes from a hull shader stage 84.

The hull shader stage 84, a tessellator stage 86, and a domain-shader 88stage comprise the tessellation stages—The tessellation stages converthigher-order surfaces to triangles, e.g., primitives, as indicated at115, for rendering within logical graphics pipeline 14. Optionally, asindicated at 111, hull shader stage 84 can generate the SRPv value foreach vertex of each generated primitive (e.g., triangle).

The geometry shader stage 90 optionally (e.g., this stage can bebypassed) processes entire primitives 22. Its input may be a fullprimitive 22 (which is three vertices for a triangle, two vertices for aline, or a single vertex for a point), a quad, or a rectangle. Inaddition, each primitive can also include the vertex data for anyedge-adjacent primitives. This could include at most an additional threevertices for a triangle or an additional two vertices for a line. Thegeometry shader stage 90 also supports limited geometry amplificationand de-amplification. Given an input primitive 22, the geometry shadercan discard the primitive, or emit one or more new primitives. Eachprimitive emitted will output an SRPv for each vertex.

The stream-output stage 92 streams primitive data from graphics pipeline14 to graphics memory 58 on its way to the rasterizer. Data can bestreamed out and/or passed into a rasterizer stage 94. Data streamed outto graphics memory 58 can be recirculated back into graphics pipeline 14as input data or read-back from the CPU 34 (FIG. 1). This stage mayoptionally stream out SRPv values to be used on a subsequent renderingpass.

The rasterizer stage 94 clips primitives, prepares primitives for apixel shader stage 96, and determines how to invoke pixel shaders.Further, as generally indicated at 118, the rasterizer stage 94 performscoarse scan conversions and determines a per-fragment variable shadingrate parameter value (SRPf) (e.g., where the fragment may be a tile, asub-tile, a quad, a pixel, or a sub-pixel region). Additionally, therasterizer stage 94 performs fine scan conversions and determines pixelsample positions covered by the fragments.

Further, as indicated at 117, the rasterizer stage 94 can also obtainlookup values (SRPm) from coarse SRP map 116. The lookup valuescorrespond to shading rates specified for a larger area, such as ascreen space of the image 24 or the entire image 24. Additionally, therasterizer stage 94 computes SRPf as a function SRPv and the lookupvalues (SRPm), as described in further detail below.

The pixel shader stage 96 receives interpolated data for primitivesand/or fragments and generates per-pixel data, such as color and samplecoverage masks.

The output merger stage 98 combines various types of pipeline outputdata (pixel shader values, depth and stencil information, and coveragemasks) with the contents of the render target 44 (FIG. 1) anddepth/stencil buffers to generate the final result of graphics pipeline14.

Also, as discussed above and as illustrated in FIG. 2, graphics pipeline14 may operate in conjunction with graphics memory 58 for exchanging andstoring data. For example, in an aspect, graphics memory 58 includes oneor more vertex buffers 100 that each contains the vertex data used todefine geometry of image 24 (or other images). Vertex data includesposition coordinates, color data, texture coordinate data, normal data,and so on. The simplest example of vertex buffer 100 is one that onlycontains position data. More often, vertex buffer 100 contains all thedata needed to fully specify 3D vertices. An example of this could bevertex buffer 100 that contains per-vertex position, normal and texturecoordinates. This data is usually organized as sets of per-vertexelements.

Further, in an aspect, graphics memory 58 may include one or more indexbuffers 102, which contain integer offsets into vertex buffers 100 andare used to render primitives 22 more efficiently. Each index buffer 102contains a sequential set of indices; each index is used to identify avertex in a vertex buffer.

Also, in an aspect, graphics memory 58 may include one or more constantbuffers 104 that allows an efficient supply of shader constants, shaderdata, and/or any other shader resources to graphics pipeline 14.Further, constant buffer 104 can be used to store the results of thestream-output stage 92. Moreover, graphics memory 58 may include one ormore texture buffers or textures data 105, such as bitmaps of pixelcolors that give an object the appearance of texture.

Additionally, in an aspect, graphics memory 58 may include one or moreunordered access resources 106 (which includes buffers, textures, andtexture arrays—without multisampling). Unordered access resources 106allow temporally unordered read/write access from multiple threads. Thismeans that this resource type can be read/written simultaneously bymultiple threads without generating memory conflicts through the use ofcertain defined functions.

Moreover, in an aspect, graphics memory 58 may include one or morerender target buffers 108, which contain the rendered target or drawingof each pixel 32 of image 24 produced by graphics pipeline 14.

As described in more detail below with respect to the method ofoperation of graphics pipeline 14 according to the described aspects,input assembler stage 80 and/or vertex shader stage 82 are configured todetermine an SRP value per vertex (SRPv) 110 for each vertex of eachprimitive 22 of image 24. For example, SRPv value 110 may be determinedfor each vertex based on one or more SRP values per object (SRPo), SRPvalues per primitive (SRPp), or SRPp values supplied by application 46(FIG. 1), e.g., at 112, and/or determined by input assembler stage 80,e.g., at 114, or based on a coarse SRP map 116. Further, rasterizerstage 94 may interpolate and quantize respective SRPv values 110 fordifferent sub-tiles or fragments 18 of each primitive 22 to define SRPvalues per fragment (SRPf) 118. Pixel shader stage 96 then launchesrespective threads and performs variable rate shading per fragment ofone or more primitives 22 based on each respective SRPf 118, therebyshading variable-area color fragments for use in rendering image 24.

Referring to FIGS. 3-1 and 4, one example of operating graphics pipeline14 according to the described aspects may be explained with reference toa method 120-1 of rendering graphics in FIG. 3-1, and with reference toimage 24 having one or more primitives 22 covering one or more tiles 20,which may include one or more sub-tiles 18 (e.g., sub-tile1 andsub-tile2) per tile 20 and/or one or more pixels 32, and correspondingcomponents of rasterizer stage 94, as identified in FIG. 4.

Step 1:

At 122-1, method 120-1 includes determining an SRP map base address andSRP vertex values SRPu and SRPv to use based on either anapplication-based source of initial SRP values, or calculated based ontessellation factors. For example, in an aspect, graphics pipeline 14and/or input assembler stage 80 or vertex shader stage 82 may beconfigured to determine an SRPv value 110 to use in subsequent graphicsprocessing based on a source of initial SRP values, based on a function,or based on calculations utilizing tessellation factors from tessellatorstage 86.

For example, in a first case, graphics pipeline 14 may receive aper-primitive shading rate parameter SRPp or per-object shading rateparameter SRPo, e.g., at 112, from application 46. In the SRPo case, theinput assembler stage 80 inputs SRPo for each object within an image 24and replicates it as an SRPp value for each primitive 22. Alternatively,input assembler stage 80 inputs a primitive description from graphicscommand 36, e.g., stored in a command buffer of graphics memory 58,where the primitive description includes an SRPp value. Accordingly,vertex shader stage 82 assigns respective SRPv values 110 for eachvertex, e.g., SRPv0=SRPp, SRPv1=SRPp, SRPv2=SRPp.

Alternatively, in a second case, graphics pipeline 14 may produce acalculated SRPv value, e.g., calculated by vertex shader stage 82. Inthis case, then vertex shader stage 82 inputs constants for an SRPfunction (e.g., xcenter=an x-axis coordinate value, ycenter=a y-axiscoordinate value, radius=a value representing the radius of the regionof interest relative to the xcenter and ycenter point, SRPscalefactor=anoptional scaling factor that may be used to scale the resulting SRPvalue, if need be). Additionally, vertex shader stage 82 inputs varyings(e.g., varying input parameters—data unique to each execution thread ofa shader—from among Xdc=X-axis coordinate value in display coordinatespace, Ydc=Y-axis coordinate value in display coordinate space, andpossibly other varying values, e.g., a surface normal), and, for eachvertex, calculates SRPv=f(Xdc, Ydc, varyings, constants, SRPscalefactor)where constants are e.g. material color and world transforms, using afunction f. Function f can produce, for example, a value that is highestat coordinate (xcenter, ycenter) and falls off to a lowest value outsidea specified radius. Specifically for this example:

SRPv=SRPscalefactor*min(1,max(0,sqrt((Xdc-xcenter)+(Ydc-ycenter)²))).

Alternatively, in a third case, graphics pipeline 14 may produce sampledSRPv values, e.g., from some prior graphics pipeline 14 processing. Inthis case, vertex shader stage 82, using input constants (base address,hscale=horizontal scale, vscale=vertical scale) performs a lookup incoarse SRP map 116. In particular, for each vertex, vertex shader stage82, calculates SRPv=lookup(base address, hscale*Xdc,vscale*Ydc)*SRPscalefactor. For instance, this lookup can be afterprojection, and such may use display coordinates. Otherwise, if notafter projection, then the lookup may additionally take into account a zcoordinate and/or perspective correction factors. In other words, inputassembler stage 80 or vertex shader stage 82 utilizes a 2D map of aviewable area at coarse resolution (e.g., coarse SRP map 116) to look upan SRPv value for each primitive vertex based on a closest point incoarse SRP map 116. The horizontal and vertical coordinate values arescaled to fit the dimensions of the coarse SRP map 116, and, optionally,the resulting SRPv values may be scaled using SRPscalefactor. In analternative, to add smoothness to the result, the lookup function mayinclude performing an interpolation between the four nearest samples inSRP map 116. The lookup may alternatively be from a 3D map whose 3^(rd)dimension is indexed on a Z (depth) value, e.g. to vary SRP based ondistance from the viewpoint.

In yet another alternative, e.g., a fourth case, graphics pipeline 14may determine SRPv values 110 from calculations based on tessellationfactors in hull shader stage 84. For example, these tessellation factorscan indicate a degree of edge complexity in the scene, and therefore adesired degree of antialiasing. In this case, vertex shader stage 82uses a maximum of (SV_TessFactor=standard value representing edgetessellation, SV_InsideTessFactor=standard value representing interiortessellation) for each patch object input to graphics pipeline 14, anduses it as SRPv for all vertices produced by tessellation within theentire patch.

Thus, the determination of the SRPv value 110 may be distributed withinthe graphics pipeline 14, e.g., at the input assembler stage 80 and/orthe vertex shader stage 82, which may be configured to determine theSRPv value 110 based on either: a) use of the SRPo for every vertex inthe object, b) use of the SRPp for every vertex of each primitive, c)use of a pass through that the software application 46 supplies as inputper vertex, or d) use of a calculated SRPv based on the map ormathematical function.

Step 2:

At 124-1, method 120-1 includes outputting vertex parameters for eachvertex. For example, vertex shader stage 82 outputs parameters such asXdc (e.g., where “dc” means display coordinates), Ydc, SRPv, and otherstandard parameters, for each vertex.

Step 3:

At 126-1, method 120-1 including assembling vertices into primitives.For example, in an aspect, graphics pipeline 14 and/or primitiveprocessor 66 instantiating a primitive assembler stage, e.g., prior togeometry shader stage 90, assembles vertices from the vertex parameters,three at a time, into triangles to form a primitive, such as primitive22.

Step 4:

At 128-1 (and additionally referring to FIG. 4), method 120-1 includescoarse scan converting each primitive using interpolators to obtainSRPt(u, v). For example, in an aspect, graphics pipeline 14 executesrasterizer stage 94 such that, for each primitive 22, coarse scanconversion is performed by a tile-walk stage 121 and/or a sub-tile walkstage 123 based on the SRPv values 26 of the vertices (SRPv0, SRPv1,SRPv2) of the respective primitive 22. The coarse scan convert utilizesinterpolators (i, j) (e.g., barycentric coordinates that apply aweighting factor between the vertices that is screen axis aligned),producing SRPul, SRPur, SRPll, SRPlr values 125 (e.g., where “ul” isupper left, “ur” is upper right, “ll” is lower left, and “lr” is lowerright) for each tile 20 intersecting primitive 22. Further, for eachtile 20 intersecting each primitive 22, rasterizer stage 94 performs thefollowing:

4.1 Determine a maximum SRP value of all tile corner SRP values and anyincluded vertices' SRP values, where the maximum is referred to as anSRPtmax value (e.g., a maximum SRPv value for the tile). For example, inan aspect, rasterizer stage 94 may include a SRPmax, quantize, and clampcomponent 129 configured to perform this functionality. Optionally tilescan be subdivided into smaller sub-tiles, e.g. 4×4 pixels, and aseparate SRPtmax can be calculated for each.

4.2 Quantize and clamp the SRPtmax value to an SRPt value 127, e.g., asampling rate value within the range of coarse and anti-aliased samplingrates that are supported by the hardware of GPU 12, such as in the rangeof 1/64 to 16, in factors of two. For example, in an aspect, SRPmax,quantize, and clamp component 129 is configured to perform thisfunctionality. At this point an SRPf value 118 (FIG. 2) is copied fromthe current tile's SRPt value 127 to be used in subsequent fine scanconversion steps, and optionally transmitted to the pixel shader stage96.

4.3 GPU 12 may determine that more information may be available tographics processing system 72 in order to more effectively reduce theamount of pixel shading being performed before pixel shader stage 96.Specifically, in addition to the per-primitive variable rate shadingbeing performed, GPU 12 may perform screen space variable rate shading(SSVRS) to reduce the amount of pixel shading to be performed by pixelshader stage 96.

In an example, when SSVRS is not used, unnecessary pixel shading may beperformed during instances of variable rate where optical distortion orfoveated rendering causes a variation in shading rate across the fieldof view. In these instances, screen space rate adjustment may be desiredto reduce the per-primitive shading rate. Even though access to screenspace distortion data in the primitive or vertex shader stage 82 stilloccurs, interpolation across primitives (e.g., triangles) may causeproblems due to tessellation requiring achievement of correct density offragments. Also, in an example, SSVRS may be performed instead of lensdistortion in per-primitive variable rate shading in order to avoidrepeated costs when shading overdrawn primitives.

In another example, SSVRS may be performed for a map that is preloadedwith motion information from previous frames to indicate areas wherefull rate shading might be wasteful due to imminent motion blur. Inanother example, SSVRS may be performed for playing game cut scenes thatuse the real time game engine. During these cut scenes, authoring timeareas using smaller shading rate may be computed and stored along withthe cut scene, as the desired level of detail may not be as high as forother scenes in the game.

In a further example, SSVRS may be performed for larger primitives suchas a ground plane that has a low level of detail texture applied to italong with scattered spots of high level of detail, or specular lightingproperties requiring high fidelity. In this example, instead of astrictly screen-locked map, the map can be looked up based on texturecoordinates interpolated in screen space from the primitive vertices.

As such, in order to perform SSVRS in one example, GPU 12 may bind abitmap (e.g., screen space texture) (i.e. coarse SRP map 116) to thescan converter (i.e., rasterizer stage 94). The bitmap may be looked upbased on one or more bits of screen or viewport x,y coordinates. Eachentry in the bitmap can describe either an absolute desired shadingrate, or a shading rate change from a specified base shading rate 137at, for example, 8×8 pixel granularity across the screen, or at a ratecorresponding to SRPt in the previous steps.

In an example, for a 4K screen, a two-bit map can utilize 32 kilobytes(KB) of storage with two bits per element, representing four possibleabsolute shading rates or delta rates from the base shading rate. Inanother example, for 32×32 pixel granularity, the storage space can bereduced to 1 KB.

Furthermore, there may not be a restriction on the lifetime of a givenmap (i.e. how many primitives that can use the current map). Forexample, the map can be the same or different for each render target.Generally, a visibility (depth buffer) is expected to be shaded at thefull pixel rate without having to perform a partial flush beforechanging the visibility, so the map could be a context state. For themap to be a context state, preload queue and the cache may be required.If the coarser granularity map is acceptable then the map could utilizea number of context registers.

Thus, at 130-1 (and additionally referring to FIG. 10), method 120-1includes looking up SRP map 116 (FIG. 2) to obtain SRPm 117. Forexample, in an aspect, graphics pipeline 14 executes rasterizer stage 94to look up the SRP map to obtain SRPm, such that, one or more look upvalues in a SRP map 116 (SRPm 117) may be identified for one or morefragments (pixels 32) within one or more primitives 22 of one or moreobjects based at least on coarse texture map coordinates. Then(optionally) the looked up SRPm can be added to the base shading rate137 stored in a register to produce the final SRP value for the relevantfragments within the designated screen region.

In an example, the map coordinates include coarse screen positioncoordinates (x, y) (i.e., SRPt(u, v). As noted above in 128-1, SRPt(u,v) is obtained based on coarse scan converting each of the one or moreprimitives using interpolated SRPm 117. Further, the rasterizer stage 94includes the SRPm lookup stage 139. In this example, the coarse tilewalker of the tile walk stage 121 needs to match the SRPm 117coarseness.

4.4 At step 132-1, fine scan conversion is performed to determine samplepositions covered within the current tile 20 or sub-tile 18 (e.g., pixelcenters or multi-sample antialiasing (MSAA) depending on the finestdesired sampling rate setting of the render target). Further, in thisexample, in order to calculate the respective SRPf 118, graphicspipeline 14 can execute rasterizer stage 94 to perform a fine scanconversion to determine the respective SRPf 118 using each of the one ormore fragments (pixels 32) of the one or more primitives usinginterpolators and SRPm 117. For example, in an aspect, rasterizer stage94 may include a fine rasterizer stage 131 configured to perform thisfunctionality.

For example, when performing SSVRS, referring to FIG. 10, an example ofcalculating fragment variable SRP values for fragments of a coarse SRPmap during a rasterization stage 94 is illustrated. In this example,graphics pipeline 14 can execute rasterizer stage 94 to calculaterespective fragment variable SRP values (SRPf 118) for each of the oneor more fragments (e.g., pixels 32) within the one or more primitives 22of one or more objects based at least on the one or more lookup values(SRPm 117) and respective base shading rates for the one or morefragments (e.g., pixels 32) within the one or more primitives 22 of oneor more objects.

In particular, for each pixel 32, graphics pipeline 14 executesrasterizer stage 94 to calculate respective fragment variable SRP values(SRPf 118) based on the base shading rate 137 and a lookup value (e.g.,SRPm 117) corresponding to the pixel 32. In an example, fragmentvariable SRP values for fragments of a coarse SRP map may be calculatedbased on the function:

SRPf=BSR×2^(SRPm[x,y])

where BSR corresponds to the base shading rate 137 for the specificfragment (e.g., pixel 32), and SRPm[x,y] corresponds to the lookup valuefor the specific fragment (pixel 32). In some examples, the base shadingrate 137 may correspond to a previous SRPf that is multiple by2^(SRPm[x,y]).

4.5 Determine the number of fragments to generate within the currenttile 20 or sub-tile 18 and the number of samples (nsamples) 30 for eachfragment generated within the current tile 20 or sub-tile 18. Forexample, in an aspect, rasterizer stage 94 or fine rasterizer stage 131may be configured to perform this functionality.

Also determine the MSAA sample mask dimensions for each fragmentgenerated within the current tile or sub-tile. Mask dimension=f(x=x-axiscoordinate, y=y-axis coordinate, SRPt value, tilewidth=a width of thetile, tileheight=a height of the tile, maxAA=a maximum antialiasingvalue). For example, in an aspect, rasterizer stage 94 or finerasterizer stage 131 may be configured to perform this functionality.

4.6 For each nsamples 30 by groupsize (e.g., grouping together allthreads that have a same number of samples 30, up to a predeterminedmaximum group size), apply sample coverage to the sample mask 133 andqueue (x, y, threadID, attributes, coverage, SRPf) to pixel shader stage96 in groups. For example, in an aspect, rasterizer stage 94 may includea thread group launcher component 135 configured to perform thisfunctionality.

Example of 4.1 and 4.2

For instance, referring to FIGS. 5 and 6, an example of identifying, bya GPU at the rasterizer stage 94 and in a graph 140, one or more SRPmvalues 117. In this example, referring specifically to graph 140 of FIG.5, identifying the SRPm values 117 is based at least on map coordinates(e.g., a, b, c, d, e, f, g, h). Further, an SRPv value is supplied, forexample, by application 46 for each vertex (e.g., v0, v1, and v2) ofprimitive 22. FIG. 5 illustrates interpolation at tile-edgeintersections (e.g., in tile 1 (T1) and tile 2 (T2)), tile corners(e.g., in T2 and tile 3 (T3)), and/or vertices (e.g., v0, v1, v2)relevant for each tile, T1, T2, and T3. In this example, each tilecomprises an 8×8 sub-tile grid, where each box in the grid represents apixel.

Referring to the table 150 of FIG. 6, for tile T1 (e.g., which includesa vertex of primitive 22), the SRPtilemax value is the maximum of theSRP values for points v1, a, and b. For tile T2 (e.g., which includesedge intersections with primitive 22), the SRPtilemax value is themaximum of the SRP values for points a, b, c, d, e, and f. For tile T3(e.g., which is completely covered by primitive 22), the SRPtilemaxvalue is the maximum of the SRP values for points e, f, g, and h.

Example of 4.4 and 4.5

Continuing with the example, referring to graph 160 of FIG. 7, an aspectof fine scanning to determine tiles covered and determining the finalnsamples and sample coverage mask is illustrated. In this example, whichfocuses on Tile T2, the SRP value is evaluated on a 4×4 sub-tile grid.In this instance, a maximum anti-aliasing (AA) for GPU 12 (and thus theconfiguration of the current render target 44) is set for 2×AA. As such,with this setting, there are a maximum of 2 coverage samples (e.g.,represented as a hollow circle and a black circle) evaluated per pixel32 everywhere over the scan by rasterizer stage 94, and 2 bits arepassed per pixel 32 in the coverage mask.

As such, out of the 8×8 sub-tile grid of pixels 161, the leftmost 4×8pixels 164 of T2 have pixel shading done at 1×AA based on the SRPf 171for that region of T2. For the tile T2, 59 of the total possible 64samples are covered; also, 30 of the 32 pixels (e.g., as represented bypixel 162) will be launched for shading (e.g., based on the colorsamples represented by the black circles) by the target sample position.For each of the 30 launched pixel shader threads, two coverage bits 164are sent. For instance, in this case, the 8×8 sub-tile grid of pixels161 may be considered a fragment comprising one color per pixel having asample coverage mask for all samples belonging to the pixel.Alternatively, for instance, the 8×8 sub-tile grid of pixels 161 may beconsidered to be one of one or more fragments within a particularregion, where each of the fragments comprise one color per one or moreof the samples per pixel and having a sample coverage mask for each ofthe one or more samples per pixel.

In contrast, for the rightmost 4×8 sub-tile grid of pixels 166, shadingis done at ½×AA rate (2 wide by 1 high) based on the SRPf 173 for thatregion, and four coverage bits 164 are sent for each of the 16 threads(corresponding to respective pairs of pixels 168) launched for shading.Thus, the operation of the described aspects on the rightmost 4×8 pixelsresults in substantial graphics processing savings. For instance, inthis case, the rightmost 4×8 sub-tile grid of pixels 166 may beconsidered one of one or more fragments within a particular region,wherein the one or more fragments comprise one color per multiple pixelsand have a sample coverage mask for all of the samples belonging to themultiple pixels.

It should be noted that, in other cases, there may be a particularregion having one or more fragments comprising one color per tile and asample coverage mask for all samples belonging to the pixels belongingto the tile.

Additionally, it should be noted that, corresponding to the above cases,there may be one or more other regions having one or more fragments thathave different colors (e.g., from the color of the above regions), e.g.,per one pixel or per one or more of the samples per pixel, and havingsimilar coverage masks as mentioned above.

Step 5:

Referring back to FIG. 4, at 134-1, method 120-1 includes shading eachpixel based on each SRPf. For example, in an aspect, graphics pipeline14 executes pixel shader stage 96 for each pixel shader thread toperform one or more of the following actions.

5.1—Determine (x, y, coverage, u, v, other attributes, SRP), where x, yare position coordinates, coverage relates to a coverage mask, the u, vvalues are texture coordinates, based on a two-dimensional array oftexture elements (texels), and where other attributes may be u,v valuesfor a second texture, or surface normal, etc.

5.2—Determine texture sampling gradients du/dx, du/dy, dv/dx, dv/dyutilizing the SRPf.

5.3—Determine texture level of detail (LOD) and degree of anisotropy.

5.4—Perform texture sampling, other shading, and generate color.

5.5—Generate Output Merger color fragment command with (x, y, coverage,color), where coverage is the coverage mask identifying the samplepositions covered by the color.

For example, in an aspect, pixel shader stage 96 calculates a color foreach queued fragment and outputs the resulting complete fragments to theoutput merger stage 98 (see method 120-1 at 136-1, explained below).Fragments that cover a single pixel 32 or portion of a single pixel 32are sent in a single command to the output merger stage 98. In anembodiment, fragments that cover multiple pixels 32 are replicated andsent a pixel at a time to the one or more output merger units thathandle particular (x,y) pixels. In another embodiment, fragments thatcover multiple pixels 32 are sent as a single command to the outputmerger stage 98, where they are stored in a fragment buffer that permitslarge fragments to be later resolved into individual pixel values. Inother words, “fragment” to refer to the color plus coverage maskproduced by the pixel shader stage 96 for a particular “region” of aprimitive 22. So a region could have a particular shading rate resultingin some number of fragments being shaded.

Example of 5.1 and 5.2

In one example of initiating the threads and determining texturesampling, referring to graphs 170 and 180 of FIGS. 8 and 9,respectively, rasterizer stage 94 can calculate gradients 172 du/dx,dv/dx, du/dy, dv/dy for dx=1 and dy=1, at each sample corresponding to apixel (e.g., pixels 0, 1, 2, and 3 in a row of the graph), independentof SRP, using neighboring u and v (sample locations identified by adashed line circle) also calculated by rasterizer stage 94 (see, e.g.,FIG. 8). In this case, “du/dx” represents a change in u (delta u) over alocal distance in x (delta x)—in other words, a fraction du/dx. Asimilar concept applies to du/dy, dv/dx, and dv/dy. For example, theX-axis gradient at pixel 0 is du/dx0, which is calculated as u1 minusu0. Also, FIG. 8 lists the respective SRP values at each vertex (e.g.,SRP0=0.5, etc.). Then, pixel shader stage 96, or pre-pass stage, canmodify these gradients to define modified gradients 182 for the shadedsamples using the respective SRPf from rasterizer stage 94 (see, e.g.,FIG. 9). For example, for sample 0, the gradient determined in FIG. 8 ismultiplied by the respective SRP for sample 0 to generate the modifiedgradient 182 (e.g., du/dx0′=du/dx0*SRP0). A similar modification is madefor the gradients at the other samples, including two gradients at somevertices that have color at two sub-pixel sample positions (e.g.,du/dx2a′ and du/dx2b′, and du/dx3a′ and du/dx3b′).

Examples of the thread groupings issued by the thread group launchercomponent 135 and processed by pixel shader stage 96 for differentshading rates are noted below in Table 1.

TABLE 1 Thread groupings # Threads/ Shading Rate group Notes Entire 8x8tile at quad rate 16 On some architectures this is only a (¼xAA) partialgroup of threads, so the maximum benefit is reduced unless can combinewith neighboring tile Entire tile at pair rate 32 Fully utilized wave(1:2 or 2:1) Entire tile at 1xAA rate 64

It should be noted that if the sample rate parameter tends to vary in apredictable, screen-oriented way, multiple render targets (MRTs) withdifferent maximum AA configurations can be used to optimize space.

Step 6:

As such, at 136-1, method 120-1 includes merging each fragment into arender target. For instance, output merger stage 98 may write eachfragment color to the current render target 44 (FIG. 1) based on theshading result. For example, output merger stage 98 may process eachcolor fragment. In particular, for each pixel and/or sample covered,output merger stage 98 can perform a depth-aware blend or write functionat an AA level of the destination render target buffer 108.

As another option, especially for fragments that cover multiple pixels,the pixel shader stage 96 can output color gradients dc/dx and dc/dyalong with a reference color c (where c can be one of red, green, orblue), so that the output merger stage 98 can either calculate itselfand store a unique color per pixel, or store the fragment along with thegradients and defer turning it into individual pixel color values untila subsequent resolve process.

In another example, referring to FIGS. 3-2 and 4, another example ofoperating graphics pipeline 14 according to the described aspects may beexplained with reference to a method 120-2 of rendering graphics in FIG.3-2, and with reference to image 24 having one or more primitives 22covering one or more tiles 20, which may include one or more sub-tiles18 (e.g., sub-tile1 and sub-tile2) per tile 20 and/or one or more pixels32, and corresponding components of rasterizer stage 94, as identifiedin FIG. 4. In particular, FIG. 3-2 corresponds to an example of when mapcoordinates include texture coordinates (u, v).

In an example, method 120-2 includes at 124-2, outputting vertexparameters for each vertex, similar to 124-1 of method 120-1 (FIG. 3-1).Further, method 120-2 includes at 126-2, assembling vertices intoprimitives 22, similar to 126-2 of method 120-2 (FIG. 3-1).

At 128-2, method 120-2 includes coarse scan converting each primitive toobtain tile (x, y) (i.e., texture coordinates). In this example,rasterizer stage 94 may determine texture coordinates based on coarsescan converting each of the one or more primitives 22 using interpolatedper-primitive parameters.

At 130-2 (and additionally referring to FIG. 10), method 120-2 includeslooking up SRP map 116 (FIG. 2) to obtain SRPm 117. For example, in anaspect, graphics pipeline 14 executes rasterizer stage 94 to look up theSRP map 116 to obtain SRPm 117, such that, one or more look up values(SRPm 117) in a SRP map 116 may be identified for one or more fragments(pixels 32) within one or more primitives 22 of one or more objectsbased at least on map coordinates. Then (optionally) the looked up SRPm117 can be added to the base shading rate 137 stored in a register toproduce the final SRP value for the relevant fragments within thedesignated screen region.

In an example, the map coordinates include texture coordinates (u, v).As noted above in 128-2, the texture coordinates are obtained based oncoarse scan converting each of the one or more primitives usinginterpolated per-primitive parameters. Further, the rasterizer stage 94includes the SRPm lookup stage 139. In this example, the coarse tilewalker of the tile walk stage 121 needs to match the SRPm 117coarseness.

In an example, method 120-2 includes at 132-2, fine scan converting eachprimitive's tile using interpolators and SRPm 117 to obtain SRPf 118,similar to 132-1 of method 120-1 (FIG. 3-1). Further, method 120-2includes at 134-2, shading based on SRPf 118, similar to 134-1 of method134-1 (FIG. 3-1). Additionally, method 120-2 includes at 136-2, mergingeach fragment into render targets, similar to 136-1 of method 120-1(FIG. 3-1).

Referring to FIG. 11, the operation of computer device 10 havinggraphics pipeline 14 according to the described aspects is explainedwith reference to a method 200 of rendering graphics on computer device10.

At 202, method 200 includes receiving a command to render primitivesthat compose an image. For example, in an aspect, GPU 12 may receivegraphics command 36 from application 46 executed by CPU 34 to renderprimitives 22 that compose image 24 on a screen of display device 40.For example, the image 24 may comprise one or more objects, and eachobject may comprise one or more primitives 22. The graphics command 36may be received, for instance, by command processor 64 via GPU driver 48and graphics API 52, as described above. In other words, receiving thecommand to render primitives that compose the image may includereceiving an SRP value per object (SRPo) for one or more objects in theimage or receiving an SRP value per vertex (SRPv) for one or morevertices in the image, and wherein determining the respective SRP valuesfor the one or more regions further comprises using selected SRPo valuesor selected SRPv values corresponding to each region.

At 204, method 200 further includes determining respective sampling rateparameter (SRP) values for one or more regions of one or more primitivesof one or more objects that compose the image. For example, in anaspect, GPU 12 may execute graphics pipeline 14 to operate inputassembler state 80, vertex shader stage 92, or some combination thereof,to determine respective sampling rate parameter (SRP) values, e.g., SRPvvalues 110, for vertices of each primitive 22 corresponding torespective regions of image 24. In one implementation, input assemblerstate 80, vertex shader stage 92, or some combination thereof, mayexecute method 120-1 (FIG. 3-1) at 122-1 and/or 124-1 to determine SRPvvalues 110 based on source of initial SRP values, or calculate SRPvvalues 110 based on tessellation factors and/or based on performing alookup in coarse SRP map 116, and output the resulting SRPv values 110for each vertex of each primitive 22 of image 24, as described above. Inother words, determining the respective SRP values for the one or moreregions may include using selected SRPo values or selected SRPv valuescorresponding to each region, or to determining the respective SRPvalues for the one or more regions based on a coarse texture map.

At 206, method 200 also includes determining at least a first SRP valuefor a first region of at least one primitive used to compose the imageand a second SRP value for a second region of the at least one primitiveused to compose the image based on the respective SRP values for therespective regions of the image. Also, at 206, the first SRP value and asecond SRP value correspond to different sample rates and are based onthe respective SRP values for respective regions of image 24. Forexample, in an aspect, GPU 12 may execute rasterizer stage 94 ofgraphics pipeline 14 to utilize at least a first SRP value, e.g., afirst SRPf value 118, for at least a first region, e.g., a firstsub-tile, and a second SRP value, e.g., a second SRPf value 118, for atleast a second region, e.g., a second sub-tile, for at least one tile 20covered by the at least one primitive 22. For instance, in oneimplementation, rasterizer stage 94 may use method 120 at 128 todetermine tile-specific and fragment-specific SRP values that areinterpolated from SRPv values 110 of each respective primitive 22. Forinstance with respect to one implementation, refer to the descriptionabove of the coarse scanning, interpolation, SRPtmax determination,quantizing and clamping, fine scan conversion and sample coveragedetermination discussed above with respect to method 120 at 128 andFIGS. 4-7.

At 208, method 200 includes identifying a first set of a first number ofsamples covered by the at least one primitive in the first region and asecond set of a second number of samples covered by the at least oneprimitive in the second region. For example, in an aspect, GPU 12 mayexecute rasterizer stage 94 of graphics pipeline 14 to generate a firstset of a first number of samples (e.g., a first set of nsamples 30)covered in the first region having the first SRP value (e.g., a firstSRPf 118, such as SRPf 171 in FIG. 7) and a second set of a secondnumber of samples (e.g., a second set of nsamples 30) covered in thesecond region having the second SRP value (e.g., a second SRPf 118, suchas SRPf 173 in FIG. 7) for one or more respective pixels 32 covered bythe at least one primitive 22. It should be noted that the first numberof samples and the second number of samples, which define a sample mask,can include as few as 1 sample per pixel and as many as 16 samples perpixel. For instance with respect to one implementation, refer to thedescription of the coarse scanning, interpolation, SRPtmaxdetermination, quantizing and clamping, fine scan conversion and samplecoverage determination discussed above with respect to method 120 at 128and FIGS. 4-7.

At 210, method 200 includes shading at least a first fragmentcorresponding to the first region based on the first set of the firstnumber of samples and the first SRP value, and at least a secondfragment corresponding to the second region based on the second set ofthe second number of samples and the second SRP value. For example, inan aspect, GPU 12 may execute pixel shader stage 96 of graphic pipeline14 is operable to shade at least a first fragment (e.g., correspondingto a first sub-tile grid 18) corresponding to the first region based onthe first set of the first number of samples (e.g., the first set ofnsamples 30) and a first SRPf 118 (e.g., SRPf 171 in FIG. 7), and asecond fragment (e.g., corresponding to a second sub-tile grid 18)corresponding to the second region based on the second set of the secondnumber of samples (e.g., the second set of nsamples 30) and a secondSRPf 118 (e.g., SRPf 173 in FIG. 7). For instance with respect to oneimplementation, refer to the description above of shading based on SRPfvalues 118 with respect to method 120 at 134 and FIGS. 5-8. Further, forexample, the shading at 210 can include performing shading and texturingof the samples covered based on the maximum SRP value per tile; andgenerating a color fragment command based on the shading and thetexturing of the samples covered.

In other words, based on this disclosure, different regions of aprimitive or an object or an image may be determined to have differentSRP values, and hence are shaded at different shading rates. Inparticular, the shading in a first region can be based on one of: (i)one color per sample; (ii) one color per pixel; or, (iii) one color permultiple pixels (e.g., including a whole tile), while the shading in asecond region can be based on a different one of (i), (ii), or (iii). Assuch, different regions can have different shading rates.

For instance, in one example, the shading of a first set of one or morefragments (e.g., including the first fragment) within the first regionmay be based on a first color per sample and a first sample coveragemask for all of the samples in the first region. And, the shading of asecond set of one or more fragments (e.g., including the secondfragment) within the second region is based on a second color per pixeland a second sample coverage mask for all of the samples belonging toeach pixel in the second region.

Also, in another example, the shading of a first set of one or morefragments (e.g., including the first fragment) within the first regionmay be based on a first color per pixel and a first sample coverage maskfor all of the samples belonging to each pixel in the first region. And,the shading of a second set of one or more fragments (e.g., includingthe second fragment) within the second region is based on a second colorper multiple pixels and a second sample coverage mask for all of thesamples belonging to the multiple pixels in the second region.

Additionally, in yet a further example, the shading of a first set ofone or more fragments (e.g., including the first fragment) within thefirst region may be based on a first color per multiple pixels and afirst sample coverage mask for all of the samples belonging to themultiple pixels in the first region. And, the shading of a second set ofone or more fragments (e.g., including the second fragment) within thesecond region is based on a second color per sample and a second samplecoverage mask for all of the samples in the second region.

Additionally, in an aspect, the shading includes outputting colorgradients and a reference color, and calculating and storing a uniquecolor per pixel based on the color gradients and the reference color(see, e.g., the above discussion relating to FIGS. 8 and 9).Alternatively, the shading may include deferring the calculating and thestoring of the unique color per pixel by storing at least one of thefirst fragment or the second fragment along with the color gradients andthe color reference.

Further, in an aspect, shading the first fragment further comprisesshading at a first shading rate relative to a maximum antialiasing ratebased on the first SRP value (e.g., SRPf 171 in FIG. 7), and shading thesecond fragment further comprises shading at a second shading raterelative to the maximum antialiasing rate based on the second SRP value(e.g., SRPf 173 in FIG. 7), wherein the second shading rate is differentfrom the first shading rate.

At 212, method 200 includes buffering the generated results, and,ultimately, resolving the pixel colors for the image based on thegenerated results. For example, in an aspect, GPU 12 can execute outputmerger stage 98 of graphics pipeline 14 to send render targets 44 torender target buffer 108. Then, GPU 12 can execute resolver component 70of graphics pipeline 14 to utilize the render targets 44 for generatingimage 24 on a screen of display device 40.

Referring to FIG. 12, for instance, an example image 220 generated bygraphics pipeline 14 according to method 200 and/or method 120 of thedisclosure includes different tiles having different shading rates (suchas, but not limited to, ¼×AA, 1×AA, 2×AA, 4×AA) depending on a level ofdetail of different portions or regions of image 220.

Thus, in summary, the described aspects enable graphics pipeline 14 ofGPU 12 to use a scan rate parameter to vary the shading rate, from 1sample/quad up to full AA. For example, in an aspect, the graphicspipeline 14 is operable for receiving a command to render one or moreprimitives of one or more objects that compose an image, and fordetermining respective sampling rate parameter (SRP) values for one ormore regions of one or more primitives or one or more objects composingthe image. Further, the graphics pipeline 14 is operable for determiningrespective vertex-specific SRP values based on the respective source ofthe SRP values, and coarse scanning and converting primitives to tilesbased on the vertex-specific SRP values. Also, the graphics pipeline 14is operable for determining a maximum SRP value per tile based on thecoarse scanning and converting. Then, the graphics pipeline 14 isoperable for fine scanning to determine position samples covered basedon the maximum SRP value per tile. Additionally, the graphics pipeline14 is operable for shading and texturing of the samples covered based onthe maximum SRP value per tile. Then, the graphics pipeline 14 isoperable for generating a color fragment command based on the shadingand texturing of the samples covered, and performing a depth-aware blendor write function at an anti-aliasing level of a destination rendertarget buffer according to the corresponding color fragment command.

Further, for example, the described aspects can enable allocating arender target at the maximum AA rate required. In some optional aspects,graphics pipeline 14 may additionally use a primitive stagemultiple-viewport technique with multiple render targets 44 to optimizethe amount of space used to store the different portions of the screenof the display device 40 at different AA rates. This includesspecialized resolve or display stage logic to produce a consistent,one-pixel-per-color frame for display.

Also, in the described aspects, the SRP parameter can be produced by anumber of methods upstream of scan converter. For example, such methodsinclude: coarse screen-aligned map (static or dynamic); vertex shaderfeeds pixel shader with results from a map generated by a previous stageor rendering pass; object based (i.e., of an object or feature in animage; based on importance, complexity of features, and/or known modeled“edginess”); computed, e.g. radius from x0,y0; use early depth pass, usedepth complexity per tile; bumpiness during vertex shading; etc.

Additionally, the described aspects involve interpolating an SRPvertex-specific value across each primitive as part of coarse (e.g., 8×8sub-tile) scan conversion. Alternatively, the described aspects may onlyconsider vertical values if a primitive is fully contained in a tile.Further, after interpolating, the described aspects include truncatingthe SRP value to factors of two and clamping the SRP value based onhardware capabilities, e.g. 1/64×AA, ¼×AA, ½×, 1×, 2×, 4×, 8×AA, 16×AA.Optionally, the described aspects may include separate SRP values for x,y dimensions, which allows for anisotropic shading.

Further, in determining the sample rate, the described aspects considerthe minimum and maximum SRP values per tile covered. In a simpledetermination, the described aspects can use the same rate for an entire8×8 sub-tile grid based on the identified SRPtmax. In another case, ifthe SRP value is constant (e.g., minimum value=maximum value), then thedescribed aspects can launch thread groups in powers of 2, which canimprove shader stage efficiency. In some cases, the described aspectsmay utilize different shading rates per respective sub-tile regions,e.g., a 4×4 pixel region. Also, in some cases, the described aspects mayissue threads to the shader stage at a maximum required rate over anentire tile, e.g., an 8×8 sub-tile grid, and then have the shader stageearly-out (e.g., discard) unused samples.

Moreover, in some implementations, the described aspects may issuefragments at coarse shading rate that includes a boosted sample coveragemask (i.e. broadcast). In other words, the color associated with thefragment may be shared by two or more pixels, thereby providingprocessing efficiencies.

It should be noted that the described aspects of graphics pipeline 14may be implemented without affecting other graphics processes. Forinstance, hierarchical Z, early Z, and Stencil processes should continueto work orthogonally. Also, depth and coverage (occlusion) passesoperate at maximum allocated AA mode, unless there is a performanceadvantage to making this coarse as well. Further, the frame bufferresolve works exactly the same as before, including any fragment-awareoptimizations.

Optionally, the described aspects may include a new way to efficientlyinform the Output Merger stage that “this color fragment is for anentire quad (e.g., 4×4 sub-tile of a tile).”

Also, in some optional implementations, the described aspects mayinclude mechanisms for how to handle texture LOD intrinsically with thedescribed variable shading rate. For example, in some case, thedescribed aspects may update the fixed-function hardware to take intoaccount the variable shading rate. In other cases, the described aspectsmay include running a “pre-pixel” shader to calculate this.Alternatively, some implementations may simply make the shader stagealways calculate it, or informing the shader stage of the parameter.

As used in this application, the terms “component,” “system” and thelike are intended to include a computer-related entity, such as but notlimited to hardware, firmware, a combination of hardware and software,software, or software in execution. For example, a component may be, butis not limited to being, a process running on a processor, a processor,an object, an executable, a thread of execution, a program, and/or acomputer. By way of illustration, both an application running on acomputing device and the computing device can be a component. One ormore components can reside within a process and/or thread of executionand a component may be localized on one computer and/or distributedbetween two or more computers. In addition, these components can executefrom various computer readable media having various data structuresstored thereon. The components may communicate by way of local and/orremote processes such as in accordance with a signal having one or moredata packets, such as data from one component interacting with anothercomponent in a local system, distributed system, and/or across a networksuch as the Internet with other systems by way of the signal.

Furthermore, various aspects are described herein in connection with adevice (e.g., computer device 10), which can be a wired device or awireless device. Such devices may include, but are not limited to, agaming device or console, a laptop computer, a tablet computer, apersonal digital assistant, a cellular telephone, a satellite phone, acordless telephone, a Session Initiation Protocol (SIP) phone, awireless local loop (WLL) station, a personal digital assistant (PDA), ahandheld device having wireless connection capability, a computingdevice, or other processing devices connected to a wireless modem.

Moreover, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or.” That is, unless specified otherwise, or clearfrom the context, the phrase “X employs A or B” is intended to mean anyof the natural inclusive permutations. That is, the phrase “X employs Aor B” is satisfied by any of the following instances: X employs A; Xemploys B; or X employs both A and B. In addition, the articles “a” and“an” as used in this application and the appended claims shouldgenerally be construed to mean “one or more” unless specified otherwiseor clear from the context to be directed to a singular form.

Various aspects or features will be presented in terms of systems thatmay include a number of devices, components, modules, and the like. Itis to be understood and appreciated that the various systems may includeadditional devices, components, modules, etc. and/or may not include allof the devices, components, modules etc. discussed in connection withthe figures. A combination of these approaches may also be used.

The various illustrative logics, logical blocks, and actions of methodsdescribed in connection with the embodiments disclosed herein may beimplemented or performed with a specially-programmed one of a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A general-purpose processormay be a microprocessor, but, in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration. Additionally, at leastone processor may comprise one or more components operable to performone or more of the steps and/or actions described above.

Further, the steps and/or actions of a method or algorithm described inconnection with the aspects disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module may reside in RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of storage mediumknown in the art. An exemplary storage medium may be coupled to theprocessor, such that the processor can read information from, and writeinformation to, the storage medium. In the alternative, the storagemedium may be integral to the processor. Further, in some aspects, theprocessor and the storage medium may reside in an ASIC. Additionally,the ASIC may reside in a computer device (such as, but not limited to, agame console). In the alternative, the processor and the storage mediummay reside as discrete components in a user terminal. Additionally, insome aspects, the steps and/or actions of a method or algorithm mayreside as one or any combination or set of codes and/or instructions ona machine readable medium and/or computer readable medium, which may beincorporated into a computer program product.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored or transmitted as one or moreinstructions or code on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that facilitates transfer of a computer programfrom one place to another. A storage medium may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionmay be termed a computer-readable medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs usually reproduce data optically withlasers. Combinations of the above should also be included within thescope of computer-readable media.

While aspects of the present disclosure have been described inconnection with examples thereof, it will be understood by those skilledin the art that variations and modifications of the aspects describedabove may be made without departing from the scope hereof. Other aspectswill be apparent to those skilled in the art from a consideration of thespecification or from a practice in accordance with aspects disclosedherein.

What is claimed is:
 1. A method of rendering graphics in a computerdevice, comprising: determining, by a graphic processing unit (GPU) at arasterization stage, map coordinates based on coarse scan converting aprimitive of an object, the map coordinates indicating a location on asampling rate parameter (SRP) map of a fragment within the primitive ofthe object; identifying, by the GPU at the rasterization stage, a lookupvalue for the fragment within the primitive of the object based at leaston the map coordinates; calculating, by the GPU at the rasterizationstage, a respective fragment variable SRP value for the fragment withinthe primitive of the object based at least on the lookup value; andshading, by the GPU at a pixel shader stage, the fragment within theprimitive of the object based on the respective fragment variable SRPvalue.
 2. The method of claim 1, wherein the map coordinates includecoarse screen position coordinates (x, y), the coarse screen positioncoordinates (x, y) being determined based on coarse scan converting theprimitive using interpolated data.
 3. The method of claim 2, furthercomprising: determining, by the GPU, respective SRP values for one ormore regions of the primitive of the object based at least on anapplication-based source of initial SRP values or one or moretessellation factors, wherein the respective SRP values corresponds to aSRP vertex value for texture coordinates (u, v); outputting, by the GPU,respective vertex parameters for each vertex based on determining therespective SRP values; and assembling, by the GPU, each vertex into theprimitive based on the respective vertex parameters.
 4. The method ofclaim 1, wherein the map coordinates include texture coordinates (u, v),the texture coordinates (u, v) being determined based on coarse scanconverting the primitive using interpolated per-primitive parameters. 5.The method of claim 4, further comprising: outputting, by the GPU,respective vertex parameters for each vertex; and assembling, by theGPU, each vertex into the primitive based on the respective vertexparameters.
 6. The method of claim 1, wherein calculating, by the GPU atthe rasterization stage, the respective fragment variable SRP value forthe one fragment within the primitive of the object based at least onthe lookup value further comprises calculating, by the GPU at therasterization stage, the respective fragment variable SRP value for thefragment within the primitive of the object based at least on the lookupvalue and a base shading rate for the fragment within the primitive ofthe object.
 7. The method of claim 1, wherein calculating, by the GPU atthe rasterization stage, the respective fragment variable SRP value forthe fragment within the primitive of the object further comprisesperforming a fine scan conversion to determine the respective fragmentvariable SRP value using at least the fragment of the primitive.
 8. Themethod of claim 1, further comprising merging, by the GPU, each of thefragment into a render target based on shading the fragment.
 9. Acomputer device, comprising: a memory; and a graphics processing unit(GPU) in communication with the memory, wherein the GPU is configuredto: determine, at a rasterization stage, map coordinates based on coarsescan converting a primitive of an object, the map coordinates indicatinga location on a sampling rate parameter (SRP) map of a fragment withinthe primitive of the object; identify, at the rasterization stage, alookup value for the fragment within the primitives of the object basedat least on the map coordinates; calculate, at the rasterization stage,a respective fragment variable SRP value for the fragment within theprimitive of the object based at least on the lookup value; and shade,at a pixel shader stage, the fragment within the primitive of the objectbased on the respective fragment variable SRP value.
 10. The computerdevice of claim 9, wherein the map coordinates include coarse screenposition coordinates (x, y), the coarse screen position coordinates (x,y) being determined based on coarse scan converting the primitive usinginterpolated data.
 11. The computer device of claim 10, wherein the GPUis further configured to: determine respective SRP values for one ormore regions of the primitive of the object based at least on anapplication-based source of initial SRP values or one or moretessellation factors, wherein the respective SRP values correspond toSRP vertex values for texture coordinates (u, v); output respectivevertex parameters for each vertex based on determining the respectiveSRP values; and assemble each vertex into the primitive based on therespective vertex parameters.
 12. The computer device of claim 9,wherein the map coordinates include texture coordinates (u, v), thetexture coordinates (u, v) being determined based on coarse scanconverting each of the primitive using interpolated per-primitiveparameters.
 13. The computer device of claim 12, wherein the GPU isfurther configured to: output respective vertex parameters for eachvertex; and assemble each vertex into the one or more primitives basedon the respective vertex parameters.
 14. The computer device of claim 9,wherein the GPU configured to calculate the respective fragment variableSRP value for the fragment within the primitive of the object based atleast on the lookup values is further configured to calculate therespective fragment variable SRP value for the fragment within theprimitive of the object based at least on the lookup value and a baseshading rate for the fragment within the primitive of the object. 15.The computer device of claim 9, wherein the GPU configured to calculate,at the rasterization stage, the respective fragment variable SRP valuefor the fragment within the primitive of the object is furtherconfigured to perform a fine scan conversion to determine the respectivefragment variable SRP value using at least the fragment of theprimitive.
 16. A computer-readable medium storing computer-executableinstructions executable by a processor for rendering graphics in acomputer device, comprising: instructions for determining, at arasterization stage, map coordinates based on coarse scan converting aprimitive of an object, the map coordinates indicating a location on asampling rate parameter (SRP) map of a fragment within the primitive ofthe object; instructions for identifying, by the GPU at therasterization stage, a lookup value for the fragment within theprimitive of the object based at least on the map coordinates;instructions for calculating, by the GPU at the rasterization stage, arespective fragment variable SRP value for the fragment within theprimitive of the object based at least on the lookup value; andinstructions for shading, by the GPU at a pixel shader stage, thefragment within the primitive of the object based on the respectivefragment variable SRP value.
 17. The computer-readable medium of claim16, wherein the map coordinates include coarse screen positioncoordinates (x, y), the coarse screen position coordinates (x, y) beingdetermined based on coarse scan converting the primitive usinginterpolated data.
 18. The computer-readable medium of claim 17, furthercomprising: instructions for determining, by the GPU, respective SRPvalues for one or more regions of the primitive of the object based atleast on an application-based source of initial SRP values or one ormore tessellation factors, wherein the respective SRP values correspondto SRP vertex values for texture coordinates (u, v); instructions foroutputting, by the GPU, respective vertex parameters for each vertexbased on determining the respective SRP values; and instructions forassembling, by the GPU, each vertex into the primitive based on therespective vertex parameters.
 19. The computer-readable medium of claim16, wherein the map coordinates include texture coordinates (u, v), thetexture coordinates (u, v) being determined based on coarse scanconverting each of the primitive using interpolated per-primitiveparameters.
 20. The computer-readable medium of claim 19, furthercomprising: instructions for outputting, by the GPU, respective vertexparameters for each vertex; and instructions for assembling, by the GPU,each vertex into the primitive based on the respective vertexparameters.